This application is in response to the NIA Pilot Research Grant Program Announcement (PA-03-108). America is rapidly aging, with more than 33 million individuals age 65 years or older. This number is expected to double in 30 years with the greatest increase among those 85 years or older 1. For a number of reasons, older adults with chronic diseases are often caught in a downward spiral of reduced muscle mass (sarcopenia), reduced functional capacity, and increased physical disability. A principal strategy to improve function in older adults has been strength-enhancing resistance training (RT); however, recent evidence suggests that traditional high-load RT results in only small to moderate effects on functional performance, with little effect on physical disability3,4. Data from our laboratory has shown that velocity, not strength, is more predictive of functional performance and disability than maximal strength 6,5, which suggests a possible alternative approach to RT. The primary aim of this research is to examine the efficacy of a novel RT protocol in functionally limited older adults at risk for subsequent physical disability. Specific aims are to: 1) examine velocity training in older adults to determine its effect on strength, velocity and muscle power output at various functional resistances, and 2) examine velocity training in older adults to determine its effect on functional performance and physical disability compared to traditional strength training. This study will be conducted as a randomized, single-blind controlled intervention trial. A 12-week laboratory-based lower extremity RT intervention will be followed by a 3-month period of self-directed exercise in a community-based setting. 53 community-dwelling men and women age 65 years or older will be randomized into one of the three study arms, velocity training (VEL), consisting of 3 sets of 8 to 10 repetitions at 40% of the one-repetition-maximum (1RM) at high velocity (ls for the concentric portion of the contraction) 3 x per week; traditional strength training (STR), consisting of 3 sets of 8 to 10 repetitions at 80% of the one-repetition-maximum (1RM) at slow velocity (2 s for the concentric portion of the contraction) 3 x per week; or control (CON), consisting of lower extremity range of motion and flexibility exercises performed 2 x per week. Outcome measures will consist of leg press (LP) and knee extension (KE) muscle strength, power and velocity across a range of functional resistances (40%-90% of maximal strength); functional performance measures consisting of dynamic balance (BAL), stair climb performance (SC), 400 meter walk (400-m W) and a short physical performance battery (SPPB); and self-reported measures of function and disability using the Late-Life Function and Disability Instrument (LLFDI). Analysis of covariance (ANCOVA) and multivariate analysis of covariance (MANCOVA) models with repeated measures will be used to compare strength, power, velocity, function and disability across groups, adjusting for baseline values. Statistical significance will be accepted at p<0.05. If velocity training proves to be a viable alternative to traditional RT, this could have a major impact on how RT is currently practiced in the community and prescribed in the clinic for functionally limited older adults. Velocity training may prove to be more effective in improving function and reducing disability and more appealing for those who have customarily avoided strenuous high-load RT. Because it is perceived as less strenuous, velocity training could have an impact on adherence to RT exercise behavior. This research will examine whether a novel approach to RT in older adults will: 1) improve muscle performance at functional resistances most frequently encountered in daily activities, and 2) improve functional performance and reduce physical disability compared to traditional strength training. This work will provide the basis for future studies to: 1) examine velocity training in different populations of physically limited older populations, and 2) explore neuromuscular mechanisms responsible for functional adaptations to this training.